Ecoregions

Temperate rainforests

May 25, 2013, 9:50 pm
Content Cover Image

Temperate rainforest in Wells Gray Provincial Park, British Columbia, Canada. (Wrin, via Wikimedia Commons)

This article draws upon the work of numerous writers, published by Ecotrust in the cited works below, and was also contributed to by Malka Geffen of Ecotrust.

caption Hoh River Temperate Rain Forest. (Source: Marietta College)

 

Temperate rainforests have been recognized as a distinct biome throughout the 20th century, although ecologists have not used the term uniformly. Most vegetation classification schemes use vegetation structure (and, secondarily, unique fauna) to define biomes, but temperate rain forests can be structurally similar to nearby forest types. Temperate rainforests are also difficult to define floristically because they share species with warmer and drier forest types.

Studying the temperate rainforests of North America, ecologist Paul Alaback defined the most widely recognized criteria for the biome: over 1400 millimeters annual precipitation, cool summers stemming from an equable year-round climate, mean annual temperature between 4 and 12 degrees Celsius, and infrequent fire.

Location and General Description

Temperate rainforests are coniferous or broadleaf forests that occur in mid-latitude areas of high rainfall. Most temperate rainforests occur where mountain ranges are close to the coast, giving rise to the term “coastal temperate rainforest.” Coastal temperate rain forests occur in the oceanic moist climates of western North America, southwestern South America, Western Europe, southeastern Australia and western New Zealand and possess remarkable ecological similarities.

Worldwide, coastal temperate rainforests are not common. Of the world’s estimated 1.3 billion hectares of temperate forest, the historic extent of coastal temperate rain forest totaled thirty to forty million hectares (2–3 percent), scarcely one-thousandth of the earth’s land surface. Tropical rain forests once covered roughly forty times more land. Though both forest types have been drastically reduced, over 30 hectares of tropical rainforest stand for every intact hectare of coastal temperate rain forest.

The largest contiguous coastal temperate rainforest traces the northwestern maritime margin of North America: from Kodiak Island in Alaska south through British Columbia to California’s redwood fogbelt. This region includes about half the remaining worldwide distribution of coastal temperate rainforest. The coastal temperate rain forests in Oregon and Washington have a distinctive dry summer season. In these forests, catastrophic fires occur every 3 to 6 centuries. By contrast, the temperate rainforests of southeastern Alaska and northern British Columbia have high annual precipitation distributed throughout the year. In this perhumid zone, wind is the dominant natural disturbance regime, while fire is comparatively rare. This zone also encompasses some of the largest remaining intact landscapes outside of the tropics.

Biodiversity Features

caption Original Global Distribution of Coastal Temperate Rain Forests. (Source: Ecotrust)

While tropical rainforests contain a diversity of plant and animal species vastly disproportionate to the area they occupy, coastal temperate rain forests contain a similarly disproportionate share of biological production. Coastal temperate rain forests accumulate and store more organic matter than any other forest type — as much as 500–2,000 metric tons of wood, foliate, leaf litter, moss, other living plants, and soil per hectare.

Temperate rainforests include some of the longest-lived and massive tree species in the world, such as coastal redwood in California, red gum in Australia and alerce in Chile. Some individual trees in temperate rain forests have grown for two millennia and surpass six meters in diameter.

All temperate rain forests have thick layers of epiphytes — plants that drape the bark, twigs and branches of dominant trees. Most of the world’s temperate rain forests are evergreen — needle-leaved in the northern hemisphere and broadleaved in the southern hemisphere — which allows these trees to actively grow throughout much of the year and minimizes nutrient demands.

The marine waters adjacent to temperate rain forests are productive as well. The upwelling zones and coldwater currents that bathe the edges of coastal temperate rain forests account for a substantial share of the biological production of the oceans. The productivity of coastal temperate rain forest ecosystems is enhanced by the nutrients and organic debris washed out of coastal watersheds, epitomizing the concept ecologists call “ecotones” — zones of transition between adjacent ecological systems. The seven anadromous species of Pacific salmon and trout, which range widely in the North Pacific before returning to their natal coastal rain forest streams to spawn, dramatically demonstrate the reciprocity of forest and sea.

Human Impacts

 

caption Original Distribution of Coastal Temperate Rain Forests. (Source: Ecotrust)

 

The fecundity and relatively mild maritime climates of coastal temperate rainforests have invited heavy exploitation. Coastal temperate rain forests were among the first landscapes logged when Euro-Americans settled North America’s Pacific Coast in the l850s. Widespread clearcut logging of old-growth conifers in this region has resulted in many rain forest valleys becoming industrial tree farms. Monocultural plantations of introduced tree species have also replaced large areas of the native forests of southern coastal Chile and New Zealand. The once-extensive coastal rain forests of the Scottish Highlands are gone, replaced by non-forested heaths and plantations of introduced Sitka spruce and lodgepole pine.

Recent actions taken for the protection of temperate rainforests around the world include the protection of the 400,000-hectare Kitlope Valley — one of the largest remaining intact coastal temperate rainforests in the world — announced by the government of British Columbia on August 16, 1994; the conservation of more than 2 million hectares in the Great Bear Rain forest announced by the government of British Columbia on February 7, 2006; and the incorporation of more than 2 million hectares of Chilean temperate rain forest into the World Network of Biosphere Reserves announced by the United Nations Educational Scientific and Cultural Organization on September 24, 2007.

Industrial exploitation of the lands and waters of the coastal temperate rainforest has meant insecure livelihoods for thousands of residents. Communities dependent on logging, mills and coastal fisheries have seen their prosperity wax and wane with the boom-and-bust cycles typical of raw materials economies. Around the world, residents are seeking to diversify local economies and to capture more of the value of the raw materials harvested and exported from the rainforest fringe.

The growing importance of recreation and tourism in the economies of many coastal areas and the recognition that conventional resource extraction depletes natural capital are forcing a reappraisal of resource-based industries. Conventional logging’s true contribution to local economies is exaggerated, for example, by the extent to which associated road building alters flows of nutrients and sediment and thereby reduces the production of coastal fisheries. Modeling of alternative silviculture practices — such as selective logging, longer rotation ages and mixed-age and species retention — suggests that active management can provide significant timber output while maintaining landscape biodiversity.

Through the retention of greater total standing biomass, these types of alternative management practices also store more carbon on the landscape. For forestland owners facing development pressures, the emerging environmental market for carbon storage may be one way to increase profitability, while ensuring the public benefits that these forests provide. Boosting the carbon stored in coastal temperate rain forests can contribute to mitigating, or offsetting, the global emissions of greenhouse gases.

Further Reading

Glossary

Citation

Silverman, H. (2013). Temperate rainforests. Retrieved from http://www.eoearth.org/view/article/156467

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